If you have diabetes, your body cannot process carbohydrates effectively.

Normally, when you eat carbs, they are broken down into small units of glucose, which end up as blood sugar.

When blood sugar levels go up, the pancreas responds by producing the hormone insulin. This hormone allows the blood sugar to enter cells.

In healthy people, blood sugar levels remain within a narrow range throughout the day. In diabetes, however, this system doesn't work the way it is supposed to.

This is a big problem, because having both too high and too low blood sugar levels can cause severe harm.

There are several types of diabetes, but the two most common ones are type 1 and type 2 diabetes. Both of these conditions can be diagnosed at any age.

In type 1 diabetes, an autoimmune process destroys the insulin-producing beta cells in the pancreas. Diabetics must inject insulin several times a day to ensure that glucose gets into the cells and stays at a healthy level in the bloodstream (4).

In type 2 diabetes, the beta cells at first produce enough insulin, but the body's cells are resistant to its action, so blood sugar remains high. To compensate, the pancreas produces more insulin, attempting to bring blood sugar down.

Over time, the beta cells lose their ability to produce enough insulin (5).

Of the three nutrients -- protein, carbs and fat -- carbs have the greatest impact on blood sugar control. This is because the body breaks them down into glucose.

Therefore, diabetics may need to take large dosages of insulin and/or diabetes medication when they eat a lot of carbohydrates.

Bottom Line: Diabetics are deficient in insulin, or resistant to its effects. When they eat carbs, their blood sugar can rise to potentially dangerous levels unless medication is taken.

The ideal carb intake for diabetics is a somewhat controversial topic, even among those who support carb restriction.

Many studies found dramatic improvements in blood sugar levels, weight and other markers when carbs were restricted to 20 grams per day (7, 8).

Dr. Richard K. Bernstein, who has type 1 diabetes, has eaten 30 grams of carbs per day and documented excellent blood sugar control in his patients who follow the same regimen (15).

However, other research shows that more moderate carb restriction, such as 70–90 grams of total carbs, or 20% of calories from carbs, is also effective (13, 16).

The optimal amount of carbs may also vary by individual, since everyone has a unique response to carbs.

According to the American Diabetes Association (ADA), there’s no one-size-fits-all diet that works for everyone with diabetes. Personalized meal plans, which take into account your dietary preferences and metabolic goals, are best (17).

The ADA also recommends that individuals work with their health care team to determine the carb intake that’s right for them.

To figure out your ideal amount of carbs, you may want to measure your blood glucose with a meter before a meal and again 1 to 2 hours after eating.

As long as your blood sugar remains below 140 mg/dL (8 mmol/L), the point at which damage to nerves can occur, you can consume 6 grams, 10 grams or 25 grams of carbs per meal on a low-carb diet.

It all depends on your personal tolerance. Just remember that the general rule is the less carbs you eat, the less your blood sugar will rise.

And, rather than eliminating all carbs, a healthy low-carb diet should include nutrient-dense, high-fiber carb sources like vegetables, berries, nuts and seeds.

Bottom Line: Carb intake between 20–90 grams per day has been shown to be effective at improving blood sugar control. However, it's best to test blood sugar before and after eating to find your personal carb limit.

Carbs in plant foods are made up of a combination of starch, sugar and fiber. Only the starch and sugar components raise blood sugar.

Fiber that is found naturally in foods, whether soluble or insoluble, does not break down into glucose in the body and does not raise blood sugar levels.

You can actually subtract the fiber from the total carb content, leaving you with the digestible or "net" carb content. For example, one cup of cauliflower contains 5 grams of carbs, 3 of which are fiber. Therefore, its net carb content is 2 grams.

Prebiotic fiber, such as inulin, has even been shown to improve fasting blood sugar and other health markers in type 2 diabetics (18).

When carbs are restricted, there is often a dramatic reduction in blood sugar.

For this reason, insulin and other medication dosages will usually need to be reduced. In some cases, they may need to be eliminated altogether.

One study reported that 17 of 21 subjects with type 2 diabetes were able to stop or reduce diabetes medication when carbs were limited to 20 grams a day (7).

In another study, type 1 diabetics consumed less than 90 grams of carbs each day. Their blood glucose control improved, and there were fewer incidences of low blood sugar because insulin dosages were significantly reduced (16).

If insulin and other medications are not adjusted for a low-carb diet, there is a high risk for dangerously low blood glucose levels, also known as hypoglycemia.

Therefore, it's important that people who take insulin or diabetes medication speak with their doctor before starting a low-carb diet.

Bottom Line: Most people will need to reduce their dosage of diabetes medication or insulin when following a low-carb diet. Failure to do so may result in dangerously low blood sugar levels.